Chlorine-containing compounds, such as chlorofluorocarbons (CFCs), have been employed as refrigerants, foam blowing agents, cleaning agents, solvents, heat transfer media, sterilants, aerosol propellants, dielectrics, fire extinguishing agents, and power cycle working fluids. Such chlorine-containing compounds have proven to be detrimental to the Earth's ozone layer. Many of the hydrofluorocarbons (HFCs), used as the substitutes of CFCs, have been found to contribute to global warming. For these reasons, there is a worldwide effort to develop new compounds that are more environmentally benign while at the same time being as effective, or more effective, from a performance standpoint.
Applicants have come to appreciate that 1,1,1,2,3-pentafluoropropene (HFO-1225ye) and 1,1,1,2-tetrafluoropropene (HFO-1234yf) are each useful in one or more of the above mentioned applications. Accordingly, compositions containing either or both fluorinated olefins are among the materials being developed for such use.
Methods for producing HFO-1234yf and HFO-1225ye are known. In one example, it is known that hexafluoropropylene (HFP) can be hydrogenated to produce 1,1,1,2,3,3-hexafluoropropane (HFC-236ea). HFC-236ea is then used as a reactant in a dehydrogenation reaction to produce HFO-1225ye. It is further known that HFO-1225ye can be hydrogenated to produce 1,1,1,2,3-pentafluoropropane (HFC-245eb) and that HFC-245eb can then be dehydrofluorinated to produce HFO-1234yf.
U.S. Pat. No. 8,013,194, the contents of which are incorporated by reference herein, further provides that HFO-1225ye and HFO-1234yf can be produced in a single facility. Most notably, it was realized that the hydrogenation of HFP can yield both HFC-236ea and HFC-245eb and that these two products can be simultaneously dehydrofluorinated to produce HFO-1225ye and HFO-1234yf, respectively. Processing conditions are taught to be adjustable, so as to favor the selective conversion of one hydrofluoroolefin over the other. Catalysts that may be used for such reactions were taught to include metal catalysts, even more preferably one or more transition metal-based catalysts (including in certain preferred embodiments transition metal halide catalysts), such as FeCl3, chromiumoxyfluoride, Ni (including Ni mesh), NiCl2, CrF3, and mixtures thereof, supported or in bulk. Other catalysts include carbon-supported catalysts, antimony-based catalysts (such as SbCl5), aluminum-based catalyst (such as AlF3, Al2O3, and fluorinated Al2O3), palladium-based catalysts, platinum-based catalysts, rhodium-based catalysts and ruthenium-based catalysts, including combinations thereof.
Other examples of methods for the production of HFO-1225ye and HFO-1234yf are set forth in, at least, U.S. Pat. No. 7,560,602, which is assigned to the assignee of the present invention and is incorporated herein by reference. This patent discloses a similar dehydrohalogenation process for producing 2,3,3,3-tetrafluoropropene (1234yf) and 1,1,1,2,3-pentafluoropropene (HFO-1225ye) by catalytic dehydrofluorination of 1,1,1,2,3-pentafluoropropane (245eb) and 1,1,1,2,3,3-hexafluoropropane (HFC-236ea), respectively. Preferred dehydrohalogenation catalysts include fluorinated chromium oxide catalysts, aluminum fluoride catalysts, ferric fluoride catalysts, mixtures of magnesium fluoride and aluminum fluoride catalysts, nickel-based catalysts, carbon based catalysts, and combinations thereof.
Alternative agents for such dehydrohalogenation reactions are also known. U.S. Patent Application Publication No. 20100029997, for example, teaches the production of hydrofluoroolefins (e.g. HFO-1234yf) by dehydrohalogenating HFC-245eb by contacting it to potassium hydroxide (KOH), sodium hydroxide (NaOH), Ca(OH)2, CaO, and combinations thereof. While, in certain embodiments, dehydrohalogenation agents include KOH, alternative agents also include LiOH, Mg(OH)2 and NaOH.
Applicants have come to appreciate that in commercial production or large scale production of fluorocarbons, such as HFO-1234yf and HFO-1225ye, reactions utilizing hydrogen present significant challenges. Hydrogenation reactions are typically highly exothermic, which creates challenges for thermal management of a large reactor system, particularly at a commercial or large manufacturing scale. Also, the ability to effectively utilize hydrogen to achieve a high conversion of the starting material is critical to an economic process. Safety in dealing with hydrogenation processes is also critical, as the temperatures of the reaction can easily reach extremely high, and unsafe, levels.